1. Field of the Invention
The present invention is directed to a multi-chamber ink-jet print cartridge (pen), and more particularly to such a pen having a unitarily-formed main body member that minimizes ink-to-ink interfaces between ink colors at mating surfaces of pen body components.
2. Description of the Related Art
Ink-jet printers commonly employ ink-jet print cartridges, or "pens," which include a sophisticated printhead and an attached ink chamber filled with a supply of ink. The printhead is a micromechanical part that contains an array of miniature thermal resistors or piezoelectric transducers that are energized to eject small droplets of ink out of an associated array of nozzles. In some cases the printhead is permanently attached to the ink supply, and in others the ink supply can be separately replaced. The pen is mounted in a carriage in the printer where the pen electrically interfaces with the printer. The printer scans the pen back and forth across the print medium (e.g., paper) as the pen ejects small droplets from the nozzles in selected matrix patterns, to thereby print a swath of the desired alphanumeric characters or graphics. After each swath of printing, the printer advances the medium incrementally to begin a new swath. Successive swaths are printed in this manner to complete the desired alphanumeric characters or graphics on the medium.
The ink in the pen must be held in the ink chamber at less than atmospheric pressure, so that the ink does not drool out of the nozzles when the nozzles are not firing. However, this negative relative pressure, or backpressure, must not be so great that air is gulped into the interior of the firing chambers, thereby causing them to "deprime" and no longer function. Various mechanisms have been devised to provide the appropriate backpressure, such as resilient bladders and combinations of springs and flexible bags. One of the most reliable backpressure systems employs a porous material, such as synthetic foam, in the ink tank. The porous material receives and retains the ink at the appropriate backpressure by capillary action. The illustrated embodiments of the present invention use such porous members for ink retention.
It has become increasingly important to make ink-jet pens as narrow as possible. The overall width of the pen influences the width of the printer and the "footprint" or amount of desk space the printer takes up. On the other hand, users of printers desire that ink-jet pens last longer, in other words, that they hold more ink. Therefore, the designer of pens must deal with the competing demands of making the pens narrower, and the need to increase the volume of ink contained in the pen.
In recent years, color printing has become increasing popular. Color ink-jet printers employ three primary colors of ink, commonly in the subtractive primary colors cyan, magenta and yellow. Some ink-jet printers use four separate pens: one for black, and one each for cyan, magenta and yellow. Other printers use two pens: one pen for black and a separate three-chamber color pen for printing in color.
In multi-chamber pens, a separate group of nozzles on the printhead is dedicated to each color. Each color of ink held in the pen must be carefully ducted to its respective nozzle group on the printhead so that the colors do not mix within the pen. Pen bodies are typically are formed of plastic parts that may be assembled by, for example, ultrasonic welds or glue. Any mating surface of these parts where inks of different colors might mix must be carefully bonded so that mixing of ink does not occur.
Despite the fact that the colored inks must be kept separate, better print quality is achieved if the nozzle groups, corresponding to the different colors, are positioned close together on the printhead. This is true because as the pen is scanned across the page, if the nozzle groups are close together, less time goes by between the ejection of the different ink colors onto the page. It is also preferable that the printhead be as small as possible because they are formed of materials that are often relatively expensive compared to other portions of the pen.
A first generation of color ink-jet pens produced by Hewlett-Packard Company (HP), the assignee of the present invention, is described in U.S. Pat. No. 4,771,295 (Baker et al.). These pens (model no. 51606A) were designed for use in HP PaintJet (TM) printers and have three internal bodies of foam for ink containment. In 51606A PaintJet color pens, the printhead is relatively wide, almost as wide as the entire pen body. The three chambers are mounted side-by-side in the scanning direction. The three corresponding nozzle groups are also arranged side-by-side on the printhead, with each nozzle group being generally below its respective ink chamber. This simple arrangement allows for a fairly direct ducting from the individual ink chambers directly downward to their corresponding nozzle groups. The main body member is molded as a single part, with openings for insertion of foam in the top of the pen body. There are two interfaces between pen parts. One occurs at the bond between the printhead and the pen body. The other interface occurs where the top cap of the pen seals against the pen body after the foam has been inserted.
A second generation of three-color ink-jet pens produced by Hewlett-Packard Company were designed for use in color versions of the popular HP DeskJet (TM) printer. In DeskJet color pens (model no. 51625A) the printhead is much narrower than the pen body and is relatively small compared to the overall size of the pen. On the printhead, two of the nozzle groups are aligned with each other in the media-advance direction, and the other nozzle group is offset slightly in the scanning direction. The ink containment chambers are transversely oriented. In other words, rather than being mounted side-by-side in the scanning direction, they are mounted side-by-side in the media-advance direction. The small printhead size, staggered nozzle pattern, and transverse orientation of the ink chambers requires a complicated manifold structure to conduct the three ink colors from their ink chambers to their respective nozzle groups on the printhead. Because of its complicated internal structure, this manifold cannot be molded unitarily with the main body member of the pen, but is molded as a separate part and then attached to the bottom of the pen. This manifold thus adds an additional ink-to-ink interface at positions of connection between parts of the pen. One ink-to-ink interface occurs where the manifold attaches to the pen body and another occurs where the printhead mounts to the manifold. As with the PaintJet 51606A pen, another interface occurs where the top cap seals against the pen body. Not only does this manifold structure increase the possibility of intermixing of inks at interfaces, but also increases material and assembly costs. Ink-jet pens are manufactured in such high volume that such manufacturing and assembly costs are very significant.
As stated, one objective in the design of multi-chamber pens is to reduce the width of the cartridge. If the ink chambers are placed side-by-side in the scanning direction, this means that the width of each ink cartridge must be correspondingly narrowed. And if the volume of ink is to increase, the dimensions of each chamber must be increased in other directions. Often the most advantageous option is to increase the size of the pen in the direction extending away from the print medium, which may be considered the height direction. However, as the width of the pen is decreased and the dimensions of the ink chambers are increased in other directions, it becomes increasingly difficult to insert foam or other ink containment devices within each ink chamber. One way of avoiding an increasingly narrow aspect ratio to each ink chamber is to transversely orient the ink chambers as is done in the 51625A DeskJet color pens. However, this option, as stated, introduces the need for a separate manifold to duct the ink from their respective chambers to the printhead.
There remains the need, therefore, for a multi-chamber ink-jet pen that minimizes the printhead size, the pen width, and the number of ink-to-ink interfaces between colors at mating parts of the pen, and yet which allows for an increased volume of ink in each ink chamber.